1. Field of the Invention
The present invention relates generally to an arrangement of automatically restoring normal operation of a latch-in (or latching) relay, and more specifically to such an arrangement which features a self restoration function by which a latch-in relay is capable of returning to a normal condition in the event that a relay armature accidentally switches from ON position to OFF position in response to an external impact or the like which is applied thereto.
2. Description of the Prior Art
It is well known in the art that a latch-in relay maintains its contacts in the last position assumed, even without coil energization. A relay armature which forms part of a latch-in relay, switches to the ON position thereof in response to a rapidly rising voltage applied to the relay. Contrarily, when the relay is to be rendered inoperative, the opposite polarity of rapidly changing voltage is applied to the relay and hence the relay armature switches back to the OFF position thereof. A relay armature implies a movable electrically conducting arm.
In the event that a latch-in or latching relay accidentally breaks its contacts after being actuated, it is necessary to again apply actuation energy to make its contacts. Such unexpected contact breaking tends to occur with a latching type relay.
One of the conventional re-energizing circuitry for use in a latching relay circuit, has been disclosed in U.S. Pat. No. 4,907,122 assigned to the same entity as the instant application.
This prior art comprises, a pulse train oscillator, an output voltage sensing and oscillator disabling circuit, etc. The output of the relay circuit is constantly monitored by the output voltage sensing and oscillator disabling circuit. In the event that a relay armature accidentally switches to the OFF position thereof in response to an external impact or the like, an abrupt potential fall at the output of the relay circuit is detected and initiates the operation of the pulse oscillator. Thus, the relay is again supplied with a fast rising voltage and hence the rely armature restores to the ON position thereof. The output sensing and oscillator disabling arrangement, detects a normal output of the relay circuit and terminates the operation of the oscillator.
However, this prior art inherently requires the pulse oscillator as well as the arrangement for initiating and disabling the operation of the oscillator depending upon the output of the relay circuit. Consequently, this known technique has encountered a problem in that the circuit arrangement is complex and bulky.